Alumina agglomerates and preparation method thereof

Abstract

The invention relates to alumina agglomerates of the type obtained by dehydrating an aluminium oxyhydroxide or hydroxide, agglomerating the alumina thus obtained, hydrothermally treating the agglomerates and calcinating same. Said agglomerates are characterised in that: the V 37 Å thereof is greater than or equal to 75 ml/100 g, preferably greater than or equal to 80 ml/100 g and, better still, greater than or equal to 85 ml/100 g; the V 0.1 μm thereof is less than or equal to 31 ml/100 g; and the V 0.2 μm thereof is less than or equal to 20 ml/100 g, preferably less than or equal to 15 ml/100 g and, better still, less than or equal to 10 ml/100 g. The invention also relates to a catalyst carrier, an intrinsic catalyst or an absorbent, in particular for use in the petroleum and petrochemical industry, comprising such alumina agglomerates. Moreover, the invention relates to methods for preparing said agglomerates.

1. Alumina agglomerates of the type obtained by the treatment of an aluminum hydroxide or oxyhydroxide, agglomeration of the alumina thus obtained, hydrothermal treatment of the agglomerates and calcination, wherein:
 they have a V 37 Å  of greater than or equal to 75 ml/100 g, 
 they have a V 0.1 μm  of less than or equal to 31 ml/100 g, 
 they have a V 0.2 μm  of less than or equal to 20 ml/100 g. 
 
     
     
       2. The alumina agglomerates as claimed in  claim 1 , wherein they have a V 1 μm  of less than or equal to 7 ml/100 g. 
     
     
       3. The alumina agglomerates as claimed in  claim 1  wherein they have a V 0.1 μm /V 0.2  μm ratio of greater than or equal to 1.5. 
     
     
       4. The alumina agglomerates as claimed in  claim 1  wherein they have simultaneously a V 37 Å  of greater than or equal to 80 ml/100 g, a V 0.1 μ m of less than or equal to 15 ml/100 g, a V 0.2 μm  of less than or equal to 10 ml/100 g, a V 1 μm  of less than or equal to 4 ml/100 g and a V 0.1 μm /V 0.2 μm  ratio of greater than or equal to 2.5. 
     
     
       5. The alumina agglomerates as claimed in  claim 1  wherein they have been obtained from dehydrated hydrargillite. 
     
     
       6. The alumina agglomerates as claimed in  claim 1  wherein they are in the form of beads. 
     
     
       7. The alumina agglomerates as claimed in  claim 1  wherein they are in the form of extruded materials. 
     
     
       8. The alumina agglomerates as claimed in  claim 1  wherein they are in the form of crushed materials. 
     
     
       9. The alumina agglomerates as claimed in  claim 1  wherein they are in the form of monoliths. 
     
     
       10. A catalyst support, especially for the petroleum or petrochemical industry, wherein it consists of alumina agglomerates as claimed in  claim 1 . 
     
     
       11. An intrinsic catalyst, especially for the petroleum or petrochemical industry wherein it consists of alumina agglomerates as claimed in  claim 1 . 
     
     
       12. An adsorbent, especially for the petroleum or petrochemical industry, wherein it consists of alumina agglomerates as claimed in  claim 1 . 
     
     
       13. A process for producing alumina agglomerates as claimed in  claim 6 , in which:
 an aluminum hydroxide or oxyhydroxide, or hydrargillite, undergoes flash dehydration in order to obtain an active alumina powder; 
 said active alumina powder undergoes a forming operation so as to obtain beads with a green fill density of between 500 and 1100 kg/m 3 , and a diameter between 0.8 and 10 mm; 
 said beads undergo a heat treatment so as to provide them with a specific surface area of between 50 and 420 m 2 /g; 
 said beads undergo a hydrothermal treatment by impregnation with water or an aqueous solution or aqueous acid solution, followed by residence in an autoclave at a temperature of above 80° C.; and 
 the agglomerates thus obtained are calcined between 500 and 1300° C. 
 
     
     
       14. The process as claimed in  claim 13 , wherein after the heat treatment that follows granulation, the alumina beads have a V 37 Å  of greater than 65 ml/100. 
     
     
       15. The process as claimed in  claim 13  wherein the active alumina powder obtained after dehydrating the aluminum hydroxide or oxyhydroxide is ground in order to obtain a powder with a median particle size d 50  of between 5 and 25 μm. 
     
     
       16. The process as claimed in  claim 13  wherein the active alumina powder obtained after dehydrating the aluminum hydroxide or oxyhydroxide is washed with water or an aqueous acid solution. 
     
     
       17. The process as claimed in  claim 13  wherein prior to the forming operation of said active alumina powder, the latter undergoes a flash operation. 
     
     
       18. The process as claimed in  claim 13  wherein during the forming of said alumina powder or of said alumina-based material, one or more pore-forming materials that disappear on heating are added to it. 
     
     
       19. The process as claimed in  claim 18 , wherein said pore-forming materials are chosen from wood flour, charcoal, sulfur, tars, plastics or emulsions of plastics, polyvinyl alcohols, naphthalene. 
     
     
       20. The process as claimed in  claim 13  wherein said hydrothermal treatment is carried out at a temperature of 150 to 270° C., for a time of greater than 45 minutes. 
     
     
       21. The process as claimed in  claim 13  wherein said hydrothermal treatment is carried out using an aqueous acid solution containing one or more mineral and/or organic acids. 
     
     
       22. The process as claimed in  claim 21 , wherein said aqueous acid solution also includes one or more compounds that can release anions capable of combining with the aluminum ions. 
     
     
       23. The process for producing alumina agglomerates as claimed in  claim 7 , in which:
 an alumina-based material is mixed and extruded in order to form it; 
 the extruded materials thus obtained are subjected to a heat treatment so as to give them a specific surface area of between 50 and 420 m 2 /g; 
 said extruded materials are subjected to a hydrothermal treatment by impregnation with water or with an aqueous solution or with an aqueous acid solution, followed by residence in an autoclave at a temperature of above 80° C.; and 
 the agglomerates thus obtained are calcined between 500 and 1300° C. 
 
     
     
       24. The process as claimed in  claim 23 , wherein said alumina-based material is dehydrated hydrargillite. 
     
     
       25. The process as claimed in  claim 23 , wherein alumina-based material comes from the precipitation of boebmite, pseudo-boehmite or bayerite, or a mixture of such materials.